The field of invention relates generally to micro-fabrication of structures. More particularly, the present invention is directed to patterning substrates in furtherance of the formation of structures.
Micro-fabrication involves the fabrication of very small structures, e.g., having features on the order of micro-meters or smaller. One area in which micro-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, micro-fabrication becomes increasingly important. Micro-fabrication provides greater process control while allowing a reduction in the minimum feature dimension of the structures formed. Other areas of development in which micro-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like.
An exemplary micro-fabrication technique is shown in U.S. Pat. No. 6,334,960 to Willson et al. Willson et al. disclose a method of forming a relief image in a structure. The method includes providing a substrate having a transfer layer. The transfer layer is covered with a polymerizable fluid composition. A mold makes mechanical contact with the polymerizable fluid. The mold includes a relief structure, and the polymerizable fluid composition fills the relief structure. The polymerizable fluid composition is then subjected to conditions to solidify and polymerize the same, forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the mold. The mold is then separated from the solid polymeric material such that a replica of the relief structure in the mold is formed in the solidified polymeric material. The transfer layer and the solidified polymeric material are subjected to an environment to selectively etch the transfer layer relative to the solidified polymeric material such that a relief image is formed in the transfer layer.
An important characteristic with accurately forming the pattern in the polymeric material is to reduce, if not prevent, adhesion of the polymeric material, and/or, transfer layer, to the mold. These are referred to as release characteristics. In this manner, the pattern recorded in the polymeric material and/or transfer layer is not distorted during separation of the mold therefrom. To improve the release characteristics, Willson et al. form a release layer on the surface of the mold. The release layer is typically hydrophobic and/or has low surface energy. The release layer adheres to the mold and to either the transfer layer or the polymeric material. Providing the transfer layer with improved release characteristics minimizes distortions in the pattern recorded into the polymeric material and/or the transfer layer that are attributable to mold separation. This type of release layer is referred to, for purposes of the present discussion, as an a priori release layer, i.e., a release layer that is solidified to the mold.
Another prior art attempt to improve release characteristics is described by Bender et al. in Multiple Imprinting in UV-based Nanoimprint Lithography: Related Material Issues, Microeletronic Engineering 61–62 (2002), pp. 407–413. Specifically, Bender et al. employ a mold having an a priori release layer in conjunction with a fluorine-treated UV curable material. To that end, a UV curable layer is applied to a substrate by spin-coating a 200 CPS UV curable fluid to form a UV curable layer. The UV curable layer is enriched with fluorine groups to improve the release characteristics.
A priori release layers, however, typically have a limited operational life. As a result, a single mold may be coated multiple times with an a priori release layer. This can result in several hours of down-time for a given mold, reducing throughput. Additionally, the molecular structure of the a priori release layer may limit the minimization of the minimum feature dimension that is printed.
There is a need, therefore, to improve the release characteristics of a mold employed in imprint lithography processes.